1. Field of the Invention
This invention relates to ballistic resistant composite articles More particularly, this invention relates to such articles having improved ballistic protection.
2. Prior Art
Ballistic articles such as bulletproof vests, helmets, structural members of helicopters and other military equipment, vehicle panels, briefcases, raincoats and umbrellas containing high strength fibers are known. Fibers conventionally used include aramid fibers such as poly(phenylenediamine terephthalamide), graphite fibers, nylon fibers, ceramic fibers, glass fibers and the like. For many applications, such as vests or parts of vests, the fibers are used in a woven or knitted fabric. For many of the other applications, the fibers are encapsulated or embedded in a composite material
In "The Application of High Modulus Fibers to Ballistic Protection" R. C. Laible et al., J. Macromol. Sci.-Chem. A7(1), pp. 295-322 1973, it is indicated on p. 298 that a fourth requirement is that the textile material have a high degree of heat resistance; for example, a polyamide material with a melting point of 255.degree. C. appears to possess better impact properties ballistically than does a polyolefin fiber with equivalent tensile properties but a lower melting point. In an NTIS publication, AD-A018 958 "New Materials in Construction for Improved Helmets", A. L. Alesi et al., a multilayer highly oriented polypropylene film material (without matrix), referred to as "XP", was evaluated against an aramid fiber (with a phenolic/polyvinyl butyral resin matrix). The aramid system was judged to have the most promising combination of superior performance and a minimum of problems for combat helmet development.
U.S. Pat. Nos. 4,403,012 and 4,457,985 disclose ballistic-resistant composite articles comprised of networks of high molecular weight polyethylene or polypropylene fibers, and matrices composed of olefin polymers and copolymers, unsaturated polyester resins, epoxy resins, and other resins curable below the melting point of the fiber.
A. L. Lastnik, et al.; "The Effect of Resin Concentration and Laminating Pressures on KEVLAR.RTM. Fabric Bonded with Modified Phenolic Resin", Technical Report NATICK/TR-84/030, June 8, 1984; disclose that an interstitial resin, which encapsulates and bonds the fibers of a fabric, reduces the ballistic resistance of the resultant composite article.